"Animal Control have seized and impounded the offending dog and an investigation is pending."
The spokesperson said further details of the incident were not yet known.
A witness who asked not to be named told Hawke's Bay Today he cycled past the woman walking her dog when he saw the offending dog exit from a nearby property and run past him to attack her and her dog.
"For a split second I thought it was coming for me but, when it shot past, I could see how angry it was."
He said someone who he believed was the owner of the offending dog arrived quickly at the scene, grabbed the dog by the collar, and calmed it down.
He said the victim looked like she was bleeding "quite badly" from leg and arm wounds.
"It looked like she tried to defend her little dog and she had her leg bitten and her arm bitten," he said.
He said a lot of people passing by stopped to help the victim, with some calling an ambulance and another offering to take her injured dog to a vet.
A police spokesperson said they received a report that a smaller dog had been seriously injured by a larger dog about 11.50am and notified dog control.